1. Field of the Invention
The present invention relates to a resin substrate, which has a substrate body and a pin serving as an input/output terminal, and more particularly to a resin substrate having a pin which can reliably be connected to a socket or another substrate.
2. Description of the Related Art
Conventionally, a structure has been known in which a pin serving as an input/output terminal is secured and stood erect on a substrate body made of an insulating material, such as resin, for example, epoxy resin, or composite material of the resin and glass fibers, the pin being secured and stood erect by using a lead and tin (hereafter xe2x80x9cPbxe2x80x94Snxe2x80x9d) soldering material, such as Pbxe2x80x94Sn eutectic solder.
As the foregoing resin substrate, a resin substrate 101 structured, for example, as shown in FIG. 6 is exemplified. A substrate body 102 of the resin substrate 101 has a resin insulating layer 103 and a circuit layer (not shown). A first main surface 102A of the resin substrate 101 has a connection pad 104 formed thereon. A solder resist layer 105 is formed to reach the edge of the connection pad 104.
The pin 11 has a large-diameter portion 111A and a shaft portion 111b and having a structure that the overall surface is applied with nickel (hereafter xe2x80x9cNixe2x80x9d) plating or gold (hereafter xe2x80x9cAuxe2x80x9d) plating (not shown). The large-diameter portion 111A of the pin 111 is secured with a soldering material 115 to be opposite to the connection pad 104 allowed to expose over the solder resist layer 105. The soldering material 115 for establishing the connection between the pin 111 and the substrate body 102 is welded to substantially the overall surface of the exposed connection pad 104 and portions of the large-diameter portion 111A and the shaft portion 111b such that the soldering material 115 forms substantially a truncated-cone fillet shape.
When the resin substrate 101 has been joined to the socket, a large gap DSA is formed between the first main surface 102A of the substrate body 102 and the upper surface SKA of the socket SK, for example, as shown in FIG. 7. When the resin substrate 101 is mounted on another substrate or the like, also a large gap is formed. The reason for this lies in that the soldering material 115 upwards moved and welded to the shaft portion 111b of the pin 111 when the pin 111 is soldered to the substrate body 102 substantially enlarges the diameter of the shaft portion 111b of the pin 111. Thus, the shaft portion 111B cannot sufficiently deeply be inserted into the socket SK or a through hole of the other substrate.
If the large gap is formed, the overall height realized after the resin substrate 101 has been joined to the socket SK or the like is enlarged excessively. Thus, a requirement for reducing the height cannot be met. The pin 111 of a type which projects over the first main surface 102A by a short length sometimes suffers from unsatisfactory reliability of the connection with the socket SK or the like. Moreover, a requirement for connecting the substrate made of the resin 101 and the socket SK or the other substrate to each other for a shortest distance cannot be met.
As the wettability between the soldering material 115 and the Au-plated layer on the surface of the pin 111 is improved, the height HSA of the soldering material 115 which upwards moves when the pin 111 is secured is enlarged. When the wettability is adjusted to reduce the height HSA of the soldering material 115 which upwards moves, it can be considered that the overall height realized after the resin substrate 101 has been joined to the socket SK or the like can be reduced.
It is an object of the present invention to provide a resin substrate with which the gap between the substrate body and another substrate or the like can be reduced when the resin substrate having a multiplicity of pins serving as input/output terminals and stood erect is joined to a socket or another substrate.
According to the present invention, there is provided a resin substrate, comprising: a substrate body made of resin or a composite material containing resin and formed into a plate-like shape which has a first main surface; and a pin having a surface on which an Au-plated layer is formed, wherein the pin is soldered to the substrate body with a soldering material mainly composed of Sn and Sb so as to be projected over the first main surface of the substrate body.
The present invention has the structure that the soldering material for securing the pin and the substrate body to each other is the soldering material mainly composed of Sn and Sb. The foregoing soldering material becomes wet with Au plating on the surface of the pin. The wettability is inferior to the Pbxe2x80x94Sn soldering material. Therefore, the foregoing soldering material, which is capable of soldering the pin to the substrate body, does not considerably upwards move along the pin.
Therefore, the portions to which the solder is welded and, the diameter of each of which is enlarged can be decreased. Hence it follows that the pin can sufficiently deeply be inserted into the socket or the through hole of another substrate. Therefore, the gap between the first main surface of the substrate body and the socket or the other substrate can be reduced. As a result, the overall height realized after the resin substrate has been joined to the socket or the like can be reduced.
The substrate body may be made of resin, such as epoxy resin, or an insulating material made of a composite material of the foregoing resin and glass fibers. The substrate body includes a laminated circuit substrate having a core substrate, on either side or two sides of which insulating layers and circuit layers are alternately laminated. As an alternative to this, a laminated circuit substrate having no core substrate and having the foregoing laminated structure is included.
The pin must have the surface on which the Au-plated layer is formed. The bonding strength of the substrate body or the like must be considered to arbitrary select the pin. The pin may be a pin in the form of the head of a nail or a pin having a large-diameter portion in an intermediate portion thereof. The material of the pin is exemplified by metal, such as covar, a 42NIxe2x80x94Fe alloy or a copper alloy. It is preferable that a Ni-plated layer is formed as the base layer for the Au-plated layer.
The soldering material must mainly be made of tin (hereafter xe2x80x9cSnxe2x80x9d) and antimony (hereafter xe2x80x9cSbxe2x80x9d). In consideration of the melting point and the bonding strength, the quantity of the foregoing elements must be determined. In addition to the elements, such as Sn and Sb, silver (hereafter xe2x80x9cAgxe2x80x9d), bismuth (hereafter xe2x80x9cBixe2x80x9d), Au, Pb, indium (hereafter xe2x80x9cInxe2x80x9d), aluminum (hereafter xe2x80x9cAlxe2x80x9d), arsenic (hereafter xe2x80x9cAsxe2x80x9d) or the like may be added in a small quantity.
In the present invention, it is preferable that the height of the pin projecting over the first main surface is 2 mm or smaller.
If the length of the pin projecting over the first main surface of the substrate body is too short, that is, if the length is 2 mm or smaller, the portion of the pin which can be inserted into the socket or the through hole of the substrate is too short to reliably connect the resin substrate to the socket or the like when upward movement of the soldering material takes place greatly. If the connector of the socket is brought into contact with the soldering material which covers the pin, the reliability of the connection sometimes deteriorates as compared with the reliability realized when the contact with the Au-plated layer is made.
The present invention, which is arranged to use the soldering material mainly composed of Sn and Sb having a poor wettability with the pin as compared with the lead-tin (hereafter xe2x80x9cPbxe2x80x94Snxe2x80x9d) soldering material, is able to prevent upward movement of the soldering material which occurs when the pin is secured. Although the portion of the pin which projects over the substrate body is short, a sufficiently long portion of the pin, which is inserted into the socket, or the through hole of the other substrate can be maintained. As a result, the resin substrate can reliably be connected to another substrate or the like.
In the present invention, it is preferable that the thickness of the Au-plate layer of the pin is 0.04 xcexcm or larger.
If the thickness of the Au-plated layer on the surface of the pin is enlarged, the soldering material is easily wetted. Thus, the height realized by the upward movement is enlarged. Therefore, when a soldering material, such as a Pbxe2x80x94Sn soldering material, having considerable wettability is used, the thickness of the Au-plated layer cannot be enlarged.
On the other hand, the present invention arranged to use the Snxe2x80x94Sb soldering material and having poor wettability is able to prevent upward movement if the Au-plated layer having a large thickness is formed. Therefore, the Au-plated layer having a large thickness of 0.04 xcexcm or larger, for example, 0.05 xcexcm or 0.1 xcexcm, can be formed to maintain the antioxidation characteristic and reliability of the connection with the socket or the like.
In the present invention, it is preferable that the quantity of Sb contained in the soldering material is 15 wt % or lower.
If the melting point of the strength material is too high, the operation for soldering the pin to the substrate body sometimes encounters deterioration in the characteristics of the substrate body, in particular, the resin insulating layer, at the soldering temperature according to the material. Moreover, the substrate body is sometimes decolored.
According to the present invention, the soldering material is mainly composed of Sn and Sb and arranged to contain Sb by 15 wt % or smaller. Therefore, the melting point of the soldering material is 280xc2x0 C. or lower. Hence it follows that the pin can be soldered to the substrate body at a low soldering temperature. As a result, a material having excellent heat resistance is not required when the soldering operation is performed. Thus, reliable connection can be performed without any deterioration in the characteristics of the substrate body. Moreover, decoloration of the substrate body can be prevented or restrained. Since wettability required to secure the pin and the substrate body to each other can sufficiently be maintained, the reliability of the connection between the pin and the substrate body can be improved.
In the present invention, it is preferable that the quantity of Sb contained in the soldering material is not less than 3 wt % nor more than 15 wt %.
When the quantity of Sb contained in the Snxe2x80x94Sb soldering material is 3 wt % or larger, deterioration in the wettability of the soldering material apparently occurs. Therefore, when the quantity of contained Sb is 3 wt % or larger, upward movement of the soldering material which takes place when the pin is secured can reliably be prevented. Hence it follows that manufacturing yield of the resin substrate can furthermore be improved.
In the present invention, it is preferable that the melting point of the soldering material is 280xc2x0 C. or lower.
As described above, if the melting point of the strength material is too high, the operation for soldering the pin to the substrate body sometimes encounters deterioration in the characteristics of the substrate body, in particular, the resin insulating layer, at the soldering temperature according to the material. Moreover, the substrate body is sometimes decolored.
Since the present invention is structured such that the melting point of the soldering material is 280xc2x0 C. or lower, a material having excellent heat resistance is not required when the pin is secured to prevent or restrain deterioration in the characteristics of the substrate body.